(1) Field of the Invention
The present invention relates to a module having an IC chip provided thereon and a packaging technique for its assembly. Detailedly, the present invention relates to a semiconductor module which can be reduced in thickness and can still provide high reliability of the peripheral parts against environmental conditions, as well as relating to the production method of the same and a module for IC cards and the like.
(2) Description of the Prior Art
Recently, IC cards having a semiconductor integrated circuit device provided thereon have been put into practice as commutation tickets for public transportation such as buses, railroads and the like, financial cards including bank cards or identification cards. Since an IC card by itself has a data processing function and a high security function, which are not provided by magnetic cards, this advantage makes its application wider.
The IC cards are categorized into three types, i.e., contact type, non-contact type and combination type having both the contact type and non-contact type functions. For the first type or the contact type IC card, it has electrodes on the opposite side on which an IC chip is provided and the electrodes come into mechanical contact with a reader/writer device as an external device and functions as a terminal to be electrically connected. In contrast, for the second type or non-contact type IC card, it has an antenna, such as winding type inlet or etching coil type inlet, and is power supplied from, and exchanges data with, a reader/writer device in a non-contact manner by electromagnetic waves received through the antenna.
Since IC cards are inmost cases held in pockets of clothes, wallets, commutation pass cases and others, there is a strong demand for them to be portable. In order to achieve the portability, it is necessary to thin the IC card module since, in general, IC cards are easy to carry if they are 1.0 mm or thinner. In order to meet the request for a thin configuration, it is necessary to make the constituents of the IC card module, specifically, the printed wiring board, IC chip, bonding wires (especially, the height of wire looping) and sealing resin as thin as possible.
However, when an attempt is made to make the print circuit board thinner, the handling performance after provision of the IC chip will deteriorate in the packaging process in module fabrication. Accordingly, about 100 μm is the production limit at present. When an IC chip is used with a typical semiconductor package such as QFP(Quad Flat Package), SOP(Small Outline Package), CSP(Chip Size Package) or the like, the product cannot but become as thick as 200 μm as a minimum. Wire looping is formed at a height of about 150 μm from the top of IC chip, so when the IC chip and wires are sealed with resin, a resin filler of about 200 μm or thicker from the IC chip surface needs to be formed.
If an attempt was made to make there elements thinner, the IC chip would-break due to a bending load and would cause a fatal defect that causes the electric circuit of the IC chip not to work. In reducing the thickness of the sealing resin, if the epoxy resin contains a lower amount of filler, the whole module becomes liable to warp due to stresses in the resin and hence presents poor flatness and smoothness for the electric terminal surface of a contact type IC card, causing contact failure with the electric connection terminal of the reader/writer device. On the other hand, if the epoxy resin contains a large amount of filler, it presents poor fluidity and will produce unfilled portions.
Sealing techniques for producing thin IC modules with the necessary mechanical strength have been disclosed in Japanese Patent Application Laid-open Hei 11 No.296638 (to be referred to as the first prior art) and Japanese Patent Application Laid-open Hei 11 No.238744 (to be referred to as the second prior art) and the like. Specifically, Patent Application Laid-open Hei 11 No.296638 (the first prior art) discloses a technique for sealing an IC chip and its peripheral parts within a concave housing while leaving a hollow therein.
The sectional structure of a module of this technique is shown in FIG. 1. The module shown in this drawing has an IC chip 4 provided on a printed wiring board 20 while electrodes of IC chip 4 are electrically connected to predetermined terminals of printed wiring board 20 by wires 5, and then covered by a concave housing 17 so as to isolate and protect IC chip 4 and wires 5 from the outside air. In this technique, a material which has a higher modulus of elasticity than that of single crystalline silicon is used for concave housing 17 so as to protect IC chip 4 and reinforce the module.
However, in this prior art, the module is encased by joining only the interface between printed wiring board 20 and concave housing 17 while IC chip 4 and wires 5 remain within the hollow. When the module of this structure is formed into an IC card module card, and subjected to distortion, twist and other mechanical tests, the interface between printed wiring board 20 and concave housing 17 may crack and water can enter through the cracks easily. Further, if an organic substrate such as of glass epoxy, polyimide or the like is employed, repeated cycles of moisture absorption, reduction in ambient temperature and condensation of the interior atmosphere will cause condensation of water around IC chip 4 and its peripheral parts inside the hollowed space since the organic substrate itself easily permits moisture to penetrate therethrough. Thus, to improve the mechanical strength against bending, warping, twisting and the like, it is necessary to provide a structure having a high enough mechanical strength.
Japanese Patent Application Laid-open Hei 11 No.238744 (the second prior art) discloses a sealing technique in which an IC chip 4 is encapsulated with an uncured sealing resin, covered with a disk, called a topping foil 18, which is cut out from an epoxy or polyimide resin film by a punching tool, and cured. The sectional module structure of this prior art is shown in FIG. 2. The module shown in this drawing is constructed by providing an IC chip 4 on a printed wiring board 20, electrically connecting terminals of printed wiring board 20 with predetermined electrodes of IC chip 4, applying a liquid resin 19 over the chip and placing a sheet, i.e., topping foil 18, so as to secure a smooth surface.
According to this technology, it is possible to improve controllability of the module thickness by placing topping foil 18 over liquid resin 19. Further, topping foil 18 also serves as a reinforcing element and hence improves the resistance against impacts.
In the method disclosed in Japanese Patent Application Laid-open Hei 11 No.296638 (the first prior art), after provision of IC chip 4 on printed wiring board 20 by the flip chip mounting process or the COB(Chip On board) wire bonding process, the IC chip 4 and its peripheral parts on the printed wiring board are sealed along the rim of concave housing 17.
However, even though the concave housing 17 is formed of a material having an extremely low permeability, if a hollow exists inside concave housing 17, moisture penetration will occur through the surface of adhesion or through printed wiring board 20, which is usually formed of glass epoxy, polyimide or other organic compounds, and the temperature in the hollow will increase. For example, if the module is used under an external environment of 30° C., 70 % RH, the moisture inside concave housing 17 soon becomes equal to that of the external environment. When cooled from this condition, the moisture therein condenses and causes electric leakage in the interconnection circuit on the IC chip 4 surface and in printed wiring board 20, resulting in operation errors.
In Japanese Patent Application Laid-open Hei 11 No.238744 (the second prior art), topping foil 18 is cut out by a punching tool and placed and cured to complete sealing. This topping foil 18 plays the role of regulating the height of the resin seal of the IC card module and provides the reinforcing function, but will not provide any contribution to protection against external environment.